The proposed work is to investigate stem cell physiology in stimulated hemopoiesis using animal models with bone marrow expansion. The mechanisms of bone marrow expansion are being investigated using a mouse model with tumor induced neutrophilia as a model for stimulated granulocytopoiesis and using phenylhydrazine treated mice as a model for stimulated erythropoiesis. Hemopoietic stem cells (CFU-c, CFU-E, BFU-E, CFU-S) are assayed from bone marrow and spleen following transplantation of the tumor or injections of phenylhydrazine. Data of these studies are not yet available, but the same studies will be conducted in the following year.